1. Field of the Invention
This invention relates to a coating liquid for an intermediate layer of an electrophotographic photoconductor that excels in coating properties, and a manufacturing method thereof. The present invention also relates to an electrophotographic photoconductor for providing images of high picture quality with no image defects, produced using the coating liquid for the intermediate layer of the electrophotographic photoconductor, and to both an electrophotographic apparatus using the coating liquid and an electrophotographic apparatus process cartridge.
2. Description of the Related Art
Conventionally, various efforts have been made to develop electrophotographic photoconductors utilizing organic photoconductive materials exhibiting outstanding properties in terms of sensitivity, thermal stability, and toxicity and the like for such inorganic materials as Se, CdS, and ZnO, as photoconductive materials used in electrophotographic photoconductors, and electrophotographic photoconductors utilizing organic photoconductive materials are now employed in many copiers and printers.
In general, in an image forming apparatus such as a printer, copier, or facsimile machine, image formation is carried out by a series of steps, namely charging step, exposing step, developing step, and transferring step. Accordingly, an apparatus for implementing such image formation comprises at least a charging device, an image exposing device, a developing device (particularly a reverse developing device), a transferring device, and an electrophotographic photoconductor. However, with an image forming apparatus having such configuration, abnormal images tend generate during a long-term continuous use.
Moreover, in recent years, a shift to digitalization has rapidly grown, and semiconductor lasers which emit monochromatic light are used in these printers and copiers to cope with the digitalization, leads a demand for photoconductors suitable for exposure by semiconductor lasers. One of the problems with photoconductors when exposed by a semiconductor laser is that of abnormal images resulting from moire caused by light interference, or the occurrence of black specks or black spots or the like resulting from the injection of holes from the photoconductive substrate to the photoconductive layer or the electric charge generating layer during reverse developing. To deal with these problems, an intermediate layer formed on the surface of the electroconductive substrate of the photoconductor has an important role to play, measures such as addition of fine particles of a metal oxide or inorganic substance to the intermediate layer to prevent moire are taken.
Examples relating to the intermediate layer mentioned above include following examples.
(1) Japanese Patent Application Laid-Open No. H11-15181/1999
(published) (Minolta): An electrophotographic photoconductor comprising a photosensitive layer on a photoconductor substrate obtained by anodizing the surface of an aluminum or aluminum alloy substrate, performing mechanical polishing, hot water sealing, thereafter applying sealing process mentioned above, or humidifying.
(2) Japanese Patent Application Laid-Open No. 10-301314/1998 (published) (Minolta): In an electrophotographic photoconductor having at least an undercoat layer and photosensitive layer on an electroconductive substrate, the undercoat layer is comprised of a heat hardened composition wherein colloidal alumina has been mixed into a certain type of organoalcoxy siloxane.
(3) Japanese Patent Application Laid-Open No. H10-90931/1998 (published) (Minolta): In an electrophctographic photoconductor having at least an undercoat layer and photosensitive layer on an electroconductive substrate, the undercoat layer is comprised of heat-treated titanium oxide in the resin.
(4) Japanese Patent Application Laid-Open No. H5-204181/1993 (published) (Konica): An electrophotographic photoconductor having an electroconductive polyaniline layer and a photosensitive layer laminated on a substrate.
(5) Japanese Patent Application Laid-Open No. H8-44096/1996 (published) (Ricoh): In an electrophotographic photoconductor comprising a photosensitive layer and an undercoat layer containing a titanium oxide and a heat hardened resin on a substrate, the volume content of the heat hardened resin contained in the undercoat layer is 0.5 to 0.6, and the average particle diameter of the titanium oxide in the undercoat layer is 0.4 μm or smaller, and a reverse development based electrophotographic apparatus utilizing the photoconductor is used.
(6) Japanese Patent Application Laid-Open No. H9-34152/1997 (published) (Konica): An electrophotographic photoconductor having an undercoat layer containing a compound selected from metal alkoxides, organic metal chelates, silane coupling agents, and reaction products thereof, and a photoconductive layer are provided in that order on an electroconductive substrate comprising a pure aluminum, an aluminum-manganese based alloy, an aluminum-magnesium based alloy, or an aluminum-magnesium-silica based alloy.
(7) Japanese Patent Application Laid-Open No. H9-292730/1997 (published) (Konica): A reverse developing electrophotographic photoconductor having an anodized layer and a photosensitive layer formed on an electroconductive substrate comprising aluminum or an aluminum alloy, the distance Sm between crests on the surface of the anodized layer is 0.3 to 250 μm with a maximum height Rt is 0.5 to 2.5 μm, and the surface gloss value in the anodized layer surface is 60 gloss or higher.
(8) Japanese Patent Application Laid-Open No. H10-83093/1998 (published) (Ricoh): An electrophotographic photoconductor having an intermediate layer containing fine titanium oxide powder in which at least zirconium oxide exists on the surface is provided in between an electroconductive substrate and a photosensitive layer.
(9) Japanese Patent Application Laid-Open No. 2000-66432 (published) (Sharp): An electrophotographic photoconductor provided by laminating an intermediate layer, an electrical charge generating layer, and an electrical charge transporting layer, in that order, on an electroconductive substrate, wherein the intermediate layer contains an adhesive resin, a carboxylate, and a titanium oxide.
With the photoconductors described in the above (1) through (9), proposals have been made for altering the configuration of or substances contained in intermediate layers formed between the electroconductive substrate and the photosensitive layer, or for providing an anodized coating film on the surface of the electroconductive substrate, and many electrophotographic photoconductors are used which have a titanium oxide contained in an intermediate layer.
However, although an intermediate layer containing a titanium oxide is formed by coating the electroconductive substrate with a coating liquid wherein the titanium oxide and a resin are dispersed in a dispersion medium, the specific gravity of a metal oxide such as the titanium oxide is larger compared to those of the resin and dispersion medium in the coating liquid. Hence, there have been problems, such as deterioration of the coating liquid after being stored for a long period of time, inability to perform uniform coating due to precipitation or cohesion of the titanium oxide particles, or marked decline in productivity due to mixture of particles in the coating film, or having to dispose of the coating liquid.
To overcome such problems, various proposals relating to dispersion methods have been made, however, no satisfying proposals have been made in terms of coating properties required for the photoconductor coating liquid. Further, related arts (1) through (9) mentioned above also fail to describe.